And since this is basically a mutation that existed in every other 40k RPG before Black Crusade I really fail to see the issue of it being overpowered or anything. There should be a way for non-Tzeentchians to get all magicky as well.
In every other 40k RPG, being a mutant is essentially a delayed death sentence. In Black Crusade, it's expected. Additionally, the "issue" of course is that you're stealing the archetypes' shtick. The whole thing that makes the Psyker and Sorcerer archetypes different from the rest is their psyker trait - make that rollable without a significant investment (say, by being devoted to a specific deity) and you might as well give everyone a chance at becoming Adroit or rerolling criticals.